(1) Field of the Invention
The invention relates to a method for coding at least one datum and a device for determining the absolute angular position of a rotating member.
(2) Prior Art
Devices for determining the absolute angular position of a rotating member are known, comprising:                a coder designed to be integral with the rotating member, said coder being arranged to deliver two pseudo sine signals;        a sensor designed to be fixed at reading distance from the coder, said sensor comprising sensitive elements that are capable of detecting the signals delivered by the coder;        a device for processing the signals issuing from the sensor, said device being arranged to deliver three digitals A, B, C, the signals A and B being representative of the angular position of the coder and the signal C comprising at least one reference pulse;        a central processing unit connected to the processing device, said unit being arranged to use the signals A, B, C on respectively one channel.        
In fact, by using the reference pulse(s), the angular position issuing from the signals A and B can be indexed to a known reference position in order to obtain an absolute angular position with respect to said reference.
Reference can be made for example to documents FR-2 845 212 and FR-2 845 213 that describe the use of such a determination system for controlling an electronic switching motor, particularly for power steering of motor vehicles by an electrical type of power steering system.
Devices for determining an angular position are also known, which are capable of supplying other data than said position, these devices generally being used to measure the speed of rotation of a motor vehicle wheel in applications of the ABS (Anti-Blocking System) type.
Reference can be made for example to document EP 1 393 082 in which the data are transmitted using pulse trains arranged between the reference pulses.
However, this type of device is only satisfactory in applications at low speed of rotation of the rotating member, failing which the time division between two reference pulses is insufficient to contain the pulse train.
In consequence, in applications at higher speed, such as those described in document FR-2 845 213, where the speed of rotation of engine may be several thousand revolutions per minute, and especially when high resolution is required, a need still exists for a determination device for coding data in a reliable manner.
To solve this problem, the use of a fourth channel will be considered, in addition to the three channels through which the signals A, B, and C are respectively delivered, via which the additional data would be transmitted. However, this addition is unsatisfactory from the economic standpoint because of the need for an additional wire, connector and interface.